The formation of voids in the stationary portion is certainly dangerous for the working of a chromatographic column and for the accuracy of the results thus obtained. Voids can arise due both to the transport and to the packaging of the column.
It is known to introduce a chromatographic cartridge, made of polyethylene or similar material, into a biaxial compressions system, which uses two pistons acting onto the cartridge ends and provided with caps having sealing means such as O-rings. Obviously, in order to avoid radial deformations, since the material the cartridge is made of is an easily deformable plastic material, the cartridge body is fitted into a cylindrical housing, which must obviously have minimum clearances. This arrangement, however, is related to a drawback, i.e. it is extremely difficult to take the cartridge out of the housing after its use. Moreover, the sealing means used can shrink, swell and there-fore alter the working of the cartridge.
According to U.S. Pat. No. 5,601,708, another possible solution consists in carrying out a pressurized chamber around the cartridge, which prevents its radial dilatation and therefore is an obstacle to the formation of voids. This system is efficient but extremely expensive, since a pressurized chamber with suitable size should be carried out for each cartridge height; moreover, pressure needs to be efficiently controlled so as to avoid the introflexion of said cartridge.
Both systems mentioned above are characterized by the application of a pressure, axially in the first case and radially in the second one, and in both cases passive control means are provided for the unused pressure component, the cylindrical housing in the first case and the caps at the ends of the pressurized chamber in the second case.